Transparent conductive film and method for producing same

Abstract

The present invention provides a transparent conductive film that maintains low resistivity even when the thickness of a transparent electrode layer formed from a conductive oxide is increased. As a result, a low resistance value can be achieved, and cracking occurs less readily during bending.　Provided is a transparent conductive film 1 in which a transparent electrode layer 40 chiefly comprising indium oxide is formed on a flexible substrate 30, wherein the transparent electrode layer 40 has a structure in which at least the three layers of a crystalline lower layer 40a, an amorphous intermediate layer 40b, and a crystalline upper layer 40c are laminated, grain boundaries are not continuous in the thickness direction across the interposed intermediate layer 40b, the lower layer 40a is at least 30 nm thick, and the intermediate layer 40b is no more than 25 nm thick.

Description

Transparent conductive film and method for producing the same

[0001] The present invention relates to a transparent conductive film in which a transparent electrode layer is formed on a flexible substrate, and a method for producing the same.

[0002] Transparent conductive films have traditionally been widely used in touch panels, solar cells, light-control devices, and other devices. However, in recent years, there has been a demand for lower resistance due to the need for larger device areas and faster response times.

[0003] In response to such demands for lower resistance in transparent conductive films, attempts have been made to lower resistance by combining a transparent electrode material made of conductive oxide with a metal material such as a metal mesh of silver or copper, but the use of a metal material in combination with the film sometimes limits its applications due to the deterioration of reliability and durability.

[0004] International Publication No. 2016 / 163323

[0005] In light of the above, increasing the thickness of the transparent electrode layer made of conductive oxide was considered as a means of reducing the resistance of transparent conductive films without using metal materials. However, simply increasing the thickness of the transparent electrode layer resulted in an increase in resistivity, making it impossible to achieve the expected low resistance value. Furthermore, the transparent electrode layer of a transparent conductive film must be resistant to cracking when the film is bent. This requirement is particularly strong for transparent conductive films used in flexible devices, but increasing the thickness of the transparent electrode layer also posed a problem, as cracks tended to occur more easily.

[0006] The present invention aims to provide a transparent conductive film that can achieve a low resistance value by maintaining low resistivity even when the film thickness of a transparent electrode layer made of a conductive oxide is increased, and that is less likely to crack when bent.

[0007] Specific means for solving the above problems include the following embodiments. <1> A transparent conductive film including a transparent electrode layer containing indium oxide as a main component formed on a flexible substrate, wherein the transparent electrode layer has a structure in which at least three layers, namely a crystalline lower layer, an amorphous intermediate layer, and a crystalline upper layer, are laminated, wherein grain boundaries are not continuous in the thickness direction across the intermediate layer, the lower layer has a film thickness of 30 nm or more, and the intermediate layer has a film thickness of 25 nm or less. <2> The transparent conductive film according to <1>, wherein the transparent electrode layer has a film thickness of 100 nm or more. <3> The transparent conductive film according to <1> or <2>, wherein the intermediate layer has a nitrogen content of 0.6 at % or more and 15 at % or less. <4> A method for producing a transparent conductive film according to any one of <1> to <3>, wherein the intermediate layer is formed by sputtering using a target containing indium oxide as a main component in an atmosphere in which a volume ratio of a carrier gas to a nitrogen gas is 250:10 to 250:300.

[0008] According to the present invention, even when the film thickness of the transparent electrode layer made of a conductive oxide is increased, a low resistivity is maintained, thereby making it possible to provide a transparent conductive film that can achieve a low resistance value and is less likely to crack when bent.

[0009] 1 is a schematic cross-sectional view of one embodiment of the transparent conductive film of the present invention; FIG. 2 is an image-processed TEM photograph of the transparent conductive film of Example 1; FIG. 3 is an image-processed TEM photograph of the transparent conductive film of Comparative Example 1;

[0010] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0011] (Transparent Conductive Film 1) A transparent conductive film 1 as one embodiment of the transparent conductive film of the present invention is formed by laminating a transparent electrode layer 40 on a flexible substrate 30, as shown in FIG.

[0012] (Substrate 30) The substrate 30 has flexibility and can be formed, for example, by laminating a functional layer 20 such as a hard coat layer or an optical adjustment layer on one or both surfaces of the transparent resin substrate 10.

[0013] (Transparent Resin Substrate 10) The transparent resin substrate 10 is a substrate that ensures the strength of the transparent conductive film 1. The transparent resin substrate 10 can be a flexible, transparent resin film. Examples of materials for the transparent resin substrate 10 include polyester resin, polyolefin resin, acrylic resin, polycarbonate resin, polyethersulfone resin, polyarylate resin, melamine resin, polyamide resin, polyimide resin, cellulose resin, and polystyrene resin. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer. Examples of acrylic resins include polymethacrylate. As the material for the transparent resin substrate, polyester resin is preferably used, and PET is more preferably used, from the viewpoints of transparency and strength, for example.

[0014] The surface of the transparent resin substrate 10 may be subjected to a surface modification treatment. Examples of surface modification treatments include corona treatment, plasma treatment, ozone treatment, primer treatment, glow treatment, and coupling agent treatment.

[0015] The thickness of the transparent resin substrate 10 is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more, from the viewpoint of ensuring the strength of the transparent conductive film 1. The thickness of the transparent resin substrate 10 is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less, from the viewpoint of ensuring the handleability of the transparent resin substrate 10 in a roll-to-roll system.

[0016] (Functional Layer 20) The substrate 30 can have a functional layer 20 on one or both sides of the transparent resin substrate 10. The functional layer 20 may be a single layer or multiple layers. A layer that imparts a desired function to the transparent conductive film can be appropriately selected and used as the functional layer 20. Examples of layers that constitute the functional layer 20 include an optical adjustment layer, an anti-reflection layer, an anti-glare layer, an easy-adhesion layer, a stress buffer layer, a hard coat layer, an easy-slip layer, an antistatic layer, a crystallization promotion layer, a crystallization rate adjustment layer, and a coating layer.

[0017] An example of a case where the functional layer 20 is a multi-layer structure is a combination of a hard coat layer and an optical adjustment layer. The hard coat layer may be laminated on at least one side of the transparent resin substrate 10, and may be laminated on both sides as needed. The hard coat layer can impart good chemical resistance and contamination resistance. The optical adjustment layer is a layer that adjusts the optical properties of the transparent conductive film 1 to suppress the pattern visibility of the transparent electrode layer 40 and ensure excellent transparency in the transparent conductive film 1.

[0018] The hard coat layer can be formed, for example, by applying an ultraviolet-curable resin such as an acrylic resin to the surface of the transparent resin substrate 10 and curing it by ultraviolet irradiation. The optical adjustment layer can be formed, for example, by applying a diluted solution of the optical adjustment composition to the surface of the hard coat layer, drying it, and then curing the optical adjustment composition by ultraviolet irradiation.

[0019] (Transparent Electrode Layer 40) The transparent electrode layer 40 is a transparent layer that exhibits excellent conductivity. The transparent electrode layer 40 can be formed on the functional layer 20.

[0020] The transparent electrode layer 40 contains indium oxide as a main component. Examples of compounds containing indium oxide include indium-containing oxides such as indium tin composite oxide (ITO), indium gallium composite oxide (IGO), indium zinc composite oxide (IZO), and indium gallium zinc composite oxide (IGZO). These composite oxides can impart uniform conductivity to the entire surface of the transparent electrode layer 40 and are preferable from the standpoint of a balance between transparency and resistance. The main component refers to the component that is contained in the transparent electrode layer 40 at the highest ratio.

[0021] When the transparent electrode layer 40 contains ITO formed from indium oxide and tin oxide, the content of tin oxide in the ITO is preferably 8% by mass or more, and more preferably 10% by mass or more, relative to the total amount of tin oxide and indium oxide, from the viewpoint of low resistivity and stable film quality. To achieve low resistance through crystallization of the ITO, the content is preferably 20% by mass or less, and more preferably 15% by mass or less. Furthermore, from the viewpoint of improving crystallinity, a portion of the transparent electrode layer having a tin oxide content of 10% by mass or less or 8% by mass or less may be provided.

[0022] Materials other than those mentioned above may be combined for the transparent electrode layer 40. Materials to be combined with the transparent electrode layer 40 include, without particular limitation, inorganic materials containing oxides or nitrides of tin, zinc, titanium, aluminum, or the like as components, carbon-based materials such as graphene, carbon nanotubes, fullerene, and diamond-like carbon, and organic transparent conductive materials such as PEDOT, as long as they satisfy the required characteristics of the device.

[0023] The film thickness of the transparent electrode layer 40 is preferably 100 nm or more, more preferably 150 nm or more, and particularly preferably 200 nm or more, from the viewpoint of ensuring high conductivity. On the other hand, from the viewpoint of optical properties and crack resistance, it is preferably 500 nm or less, more preferably 350 nm or less, and particularly preferably 250 nm or less. Therefore, the film thickness of the transparent electrode layer 40 is preferably 100 nm or more and 500 nm or less, more preferably 150 nm or more and 350 nm or less, and particularly preferably 200 nm or more and 250 nm or less. The film thickness of the transparent electrode layer 40 can be measured by cross-sectional observation using, for example, a transmission electron microscope (TEM).

[0024] The transparent electrode layer 40 has a structure in which at least three layers, a crystalline lower layer 40a, an amorphous intermediate layer 40b, and a crystalline upper layer 40c, are stacked. The transparent electrode layer 40 is not limited to being formed of only the above-mentioned three layers, the lower layer 40a, the intermediate layer 40b, and the upper layer 40c. In other words, an additional layer for constituting the transparent electrode layer 40 may be provided between the substrate 30 and the lower layer 40a or on the upper layer 40c.

[0025] The fact that the lower layer 40a is crystalline, the middle layer 40b is amorphous, and the upper layer 40c is crystalline can be confirmed by a TEM dark-field image or bright-field image taken of a cross section perpendicular to the film surface of the transparent electrode layer 40.

[0026] Crystalline materials can be observed using TEM dark-field imaging. Dark-field imaging is an image of electron beams diffracted at a specific angle, so diffraction does not occur in amorphous areas, and only crystals oriented at a specific angle diffract. Therefore, brightly imaged areas in the dark-field image can be identified as crystalline materials.

[0027] Crystalline materials can also be observed by confirming the presence of grain boundaries in a bright-field TEM image. Since amorphous materials do not have grain boundaries, regions with grain boundaries can be confirmed as crystalline.

[0028] In this specification, the term "crystalline" includes those that partially contain amorphous parts, and "amorphous" does not include crystalline parts.

[0029] The intermediate layer 40b of the transparent electrode layer 40 is amorphous and does not contain crystal grains, so the grain boundaries formed in the lower layer 40a and upper layer 40c of the transparent electrode layer 40 are discontinuous in the intermediate layer 40b.

[0030] By appropriately setting the film formation conditions, the lower layer 40a and the upper layer 40c constituting the transparent electrode layer 40 can form a crystal structure strongly oriented in the (222) plane defined by X-ray diffraction (XRD). The (222) plane is a crystal plane parallel to the substrate surface.

[0031] The thickness of the lower layer 40a is 30 nm or more, preferably 30 nm to 150 nm, more preferably 40 nm to 130 nm, and particularly preferably 50 nm to 120 nm. The thickness of the intermediate layer 40b is 25 nm or less, preferably 4 nm to 25 nm, more preferably 5 nm to 20 nm, and particularly preferably 6 nm to 15 nm. The thickness of the upper layer 40c is preferably 30 nm or more, more preferably 30 nm to 150 nm, more preferably 40 nm to 130 nm, and particularly preferably 50 nm to 120 nm.

[0032] It is preferable to adjust the nitrogen content in each layer. The nitrogen content in the lower layer 40a is preferably 0.6 at% or less, more preferably 0.1 at% or less, and particularly preferably 0.01 at% or less. The nitrogen content in the intermediate layer 40b is preferably 0.6 at% or more and 15 at% or less, more preferably 1.0 at% or more and 10 at% or less, and particularly preferably 1.5 at% or more and 5 at% or less. The nitrogen content in the upper layer 40c is preferably 0.6 at% or less, more preferably 0.1 at% or less, and particularly preferably 0.01 at% or less.

[0033] (Formation of Transparent Electrode Layer 40) The transparent electrode layer 40 is formed by sputtering using a target containing indium oxide as a main component.

[0034] When transparent electrode layer 40 is formed using ITO as a target, the sintered density of ITO is preferably 99% or more from the viewpoint of discharge stability.

[0035] The sputtering system used can be a batch system, a roll-to-roll system, or the like, without any particular limitation, but from the viewpoint of productivity, it is preferable to use a take-up sputtering system and perform the sputtering in a roll-to-roll system. The power source used for sputtering film formation is not particularly limited, and a DC power source, an MF power source, an RF power source, or the like can be used, but from the viewpoint of improving productivity, a DC power source or an MF power source is preferred, and a DC power source is particularly preferred.

[0036] It is known that water molecules are adsorbed in a chamber that is open to the atmosphere. The water molecules in the chamber are taken into the film during the formation of the transparent electrode layer, and can be a factor in increasing the resistance. Therefore, after the film substrate is placed in the sputtering deposition apparatus, it is preferable to evacuate the chamber and reduce the water pressure in the chamber before forming the transparent electrode layer. The water pressure in the chamber is 1×10 －３ Pa or less is preferable, and 1×10 －４ Pa or less is more preferable.

[0037] The substrate may be heated or cooled during sputtering depending on the purpose. If the thermal load on the substrate due to sputtering is large, the substrate may be cooled, or sputtering may be performed while heating the substrate in order to improve the film quality of the transparent electrode layer.

[0038] The transparent electrode layer 40 includes at least three layers: a lower layer 40 a, an intermediate layer 40 b, and an upper layer 40 c. When forming multiple layers, sputtering may be performed by repeatedly discharging using the same target, or may be performed by using an apparatus comprising multiple targets and transporting them in a single operation. When an apparatus comprising multiple targets is used, the targets may be placed in separate deposition chambers, which facilitates control of pressure, etc.

[0039] Film formation by sputtering is carried out by introducing argon as a carrier gas into a film formation chamber, and further introducing oxygen gas and nitrogen gas as a doping gas. The pressure in the film formation chamber can be adjusted by the amount of carrier gas introduced. The pressure (total pressure) in the film formation chamber is preferably 0.1 Pa to 1.0 Pa, more preferably 0.25 Pa to 0.80 Pa.

[0040] The intermediate layer 40b can be efficiently doped with nitrogen by introducing nitrogen gas into the deposition chamber. The volume ratio of the carrier gas to the nitrogen gas can be controlled using a control device such as a pressure adjusting mechanism and / or a flow rate control mechanism.

[0041] In forming the intermediate layer 40b, the volume ratio of the carrier gas to the nitrogen gas is 250:10 to 250:300, preferably 250:30 to 250:250, more preferably 250:50 to 250:200, and particularly preferably 250:70 to 250:150. In order to efficiently amorphize the intermediate layer 40b, it is preferable to introduce only the carrier gas and nitrogen gas into the deposition chamber.

[0042] The transparent electrode layer 40 formed by sputtering is primarily an amorphous layer, but annealing is preferred because it increases the crystallinity, thereby reducing resistivity and improving transmittance. The annealing temperature is preferably 120 to 220°C, and more preferably 130 to 180°C. If the annealing temperature is too low, the time required for crystallization will be long, reducing productivity, while if it is too high, the temperature will exceed the heat resistance temperature of the substrate, making it impossible to maintain the shape of the film.

[0043] (Uses of Transparent Conductive Film) The transparent conductive film of the present invention can be used as a transparent electrode for displays, light-emitting devices, photoelectric conversion devices, and the like.

[0044] Example 1 A 125 μm thick optical PET film (Lumirror, manufactured by Toray Industries, Inc.) was used as a substrate, and a 2 μm thick hard coat layer was formed on both sides of the film using an ultraviolet curable resin (Lioduras TYAB, manufactured by Toyochem Co., Ltd.). The hard coat was formed by applying a UV curable resin coating solution diluted with methyl isobutyl ketone (MIBK) using a bar coater, drying in a hot air drying oven at 80°C for 1 minute, and then irradiating the film with 400 mJ / cm using a high-pressure mercury lamp. ２ This step was carried out on both sides to obtain a film with a hard coat layer, in which a hard coat layer was formed on both sides of the substrate.

[0045] Subsequently, an optical adjustment layer was formed on one side of the PET film with the hard coat layer. A UV-curable resin coating liquid for the optical adjustment layer (Lioduras TYZ, manufactured by Toyochem Co., Ltd.) with a refractive index of 1.65 was diluted with MIBK and applied by bar coating. The coating was dried in a hot air drying oven at 80°C for 1 minute, and then irradiated with 600 mJ / cm using a high-pressure mercury lamp. ２ The coating film was cured by irradiation with ultraviolet light of 1000 kJ / cm. The optical adjustment layer thus obtained had a film thickness of 40 nm.

[0046] Subsequently, a transparent electrode layer made of ITO was formed on the optical adjustment layer of the film with the optical adjustment layer by sputtering. After the film with the optical adjustment layer was placed in a roll-to-roll sputtering device, it was transported at room temperature while the water pressure in the chamber was 1×10 －４ The chamber was then evacuated to a vacuum of 0.4 Pa. Next, using ITO (tin oxide content 10.0% by mass) as a target, only argon was introduced so that the pressure inside the chamber was 0.4 Pa, and pre-sputtering was performed for 15 minutes at a discharge power of 1.0 kW. After that, while the film was being transported so that the film thickness of the base transparent electrode layer was 6 nm, sputtering was performed using a DC power supply at a discharge power of 0.2 kW, thereby forming a base transparent electrode layer.

[0047] Next, argon and oxygen were supplied at a ratio of 250:3, and under conditions of a chamber pressure of 0.3 Pa, the film was transported so that the film thickness of the first transparent electrode layer was 97 nm, and sputtering was performed using a DC power supply with a discharge power of 1.0 kW to form a first transparent electrode layer.

[0048] Next, only argon and nitrogen were supplied so that the ratio of argon to nitrogen was 250:80, and the chamber pressure was kept at 0.5 Pa. While transporting the film so that the thickness of the intermediate layer was 12 nm, sputtering was performed using a DC power supply with a discharge power of 0.2 kW to form an intermediate layer.

[0049] Next, oxygen was supplied to a ratio of argon:oxygen of 500:3, and under conditions of a chamber pressure of 0.6 Pa, the film was transported so that the film thickness of the second transparent electrode layer was 97 nm, and sputtering was performed using a DC power supply with a discharge power of 1.0 kW to form a second transparent electrode layer.

[0050] The obtained transparent conductive film was further annealed in a hot air drying oven at 140° C. for 90 minutes.

[0051] Cross-sectional STEM observation confirmed the presence of an intermediate layer separated by an interface and a grain boundary in the thickness direction that was discontinuous due to the intermediate layer. The maximum crystal orientation was the (222) peak that appeared around 30.4 degrees.

[0052] The crystal orientation of the transparent conductive film was measured using a RIGAKU X-ray diffractometer SmartLab with a parallel optical system by the out-of-plane θ / 2θ method under the conditions of a measurement range of 2θ = 25 to 65°, a step width of 0.01°, and a scan speed of 0.5° / min.

[0053] Example 2 A transparent conductive film was produced in the same manner as in Example 1, except that the film thickness of each of the first transparent electrode layer and the second transparent electrode layer was 70 nm. Cross-sectional STEM observation confirmed an intermediate layer separated by an interface and grain boundaries in the thickness direction that were discontinuous due to the intermediate layer. No crystal grains were observed inside the intermediate layer. The maximum crystal orientation was the (222) peak appearing near 30.4 degrees.

[0054] Comparative Example 1 A transparent conductive film was produced in the same manner as in Example 1, except that nitrogen was not introduced during the formation of the intermediate layer. Cross-sectional STEM observation confirmed that the intermediate layer was partially separated by an interface, but that the crystal grains of the first transparent electrode layer and the second transparent electrode layer were continuous in the thickness direction, resulting in portions where the intermediate layer could not be clearly observed. No crystal grains were observed within the intermediate layer. Furthermore, in portions where the crystal grains were continuous in the thickness direction, it was confirmed that the crystal grain boundaries were continuous in the thickness direction from the top of the underlying transparent electrode layer to the surface of the transparent electrode layer. The maximum crystal orientation was the 222 peak appearing near 30.4 degrees.

[0055] Comparative Example 2 A transparent conductive film was produced in the same manner as in Example 1, except that no intermediate layer was formed. Cross-sectional STEM observation revealed that no intermediate layer was observed between the first and second transparent electrode layers, that the crystal grains were continuous in the thickness direction, and that the crystal grain boundaries were continuous in the thickness direction from the top of the underlying transparent electrode layer to the surface of the transparent electrode layer. The maximum crystal orientation was the (222) peak appearing around 30.4 degrees.

[0056] Comparative Example 3 A transparent conductive film was produced in the same manner as in Example 1, except that the first transparent electrode layer and the intermediate layer were not formed, and the film thickness of the second transparent electrode layer was 200 nm. Cross-sectional STEM observation confirmed that the crystal grains were continuous in the thickness direction, and that the crystal grain boundaries were continuous in the thickness direction from the top of the underlying transparent electrode layer to the surface of the transparent electrode layer. The crystal orientation had a maximum (222) peak appearing around 30.4 degrees.

[0057] (Reference Example 1) A transparent conductive film was produced in the same manner as in Example 1, except that the first transparent electrode layer and the intermediate layer were not formed, and the film thickness of the second transparent electrode layer was 146 nm. Cross-sectional STEM observation confirmed that the crystal grains were continuous in the thickness direction, and that the crystal grain boundaries were continuous in the thickness direction from the top of the underlying transparent electrode layer to the surface of the transparent electrode layer. The crystal orientation had a maximum (222) peak appearing around 30.4 degrees.

[0058] (Evaluation Methods) The transparent conductive films of Examples 1 and 2, Comparative Examples 1 to 3, and Reference Example 1 were evaluated by the following evaluation methods.

[0059] The film thickness and grain boundaries of each layer of the transparent conductive layer were evaluated using a Zeiss CrossBeam 550 focused ion beam (FIB-SEM) device. Samples were cross-sectioned at an acceleration voltage of 30 kV and then finished at 5 kV. A Hitachi High-Technologies HD-2700 scanning transmission electron microscope was used to observe the cross section of the film over a range of 300 nm in the in-plane direction at an acceleration voltage of 200 kV. The presence of grain boundaries was determined by using both bright-field and dark-field images to emphasize the contrast of the crystal grains. Crystallinity was determined as crystalline when crystal grains were observed within the layer, and amorphous when no crystal grains were observed.

[0060] The maximum nitrogen concentration in the transparent electrode layer was measured by dynamic SIMS using an ADEPT1010 manufactured by PHI Corporation under the conditions of primary ion species Cs+, primary ion energy 2 eV, and secondary ion polarity Negative, with N as the element of interest. Measurement values ​​were detected every 0.7 nm, and the detection sensitivity of N was converted based on the sensitivity in ZnO. The conversion to at% was performed using an ITO density of 7.12 g / cm. ３ The measurements were carried out under the assumption that the electron gun was used for charge compensation during the measurements.

[0061] The film thickness of the transparent electrode layer was calculated by cross-sectional TEM analysis.

[0062] The sheet resistance of the transparent conductive film was calculated in accordance with JIS K7194 using Loresta GP manufactured by Mitsubishi Chemical Corporation.

[0063] The total light transmittance of the transparent conductive film was measured in accordance with JIS K7361 using a turbidity meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0064] The bending resistance of the transparent conductive film was evaluated by cutting a transparent conductive film into a 50 mm x 10 mm strip with the MD direction as the long side, wrapping it around a pin gauge with the transparent electrode layer facing inward, and holding it for 30 seconds, then visually checking for the occurrence of cracks. If no cracks occurred, the same test was repeated with the thickness of the pin gauge wrapped around it reduced by 1 mm each time, and the diameter of the smallest pin gauge that did not cause cracks was recorded as the minimum bending diameter.

[0065]

[0066] As shown in Table 1, it was confirmed that Examples 1 and 2 exhibited good resistivity and were less susceptible to cracking when bent.

[0067] Fig. 2 shows a cross-section of the transparent conductive film of Example 1. Since the intermediate layer 40b of the transparent electrode layer 40 of Example 1 is amorphous and does not contain crystal particles, the grain boundaries (shown as dotted lines in the figure) formed between the lower layer 40a and the upper layer 40c are discontinuous in the intermediate layer 40b. On the other hand, Fig. 3 shows a cross-section of the transparent conductive film of Comparative Example 1, and it was confirmed that in the portion where the crystal grains are continuous in the thickness direction, the grain boundaries (shown as dotted lines in the figure) are continuous in the thickness direction from the top of the underlying transparent electrode layer to the surface of the transparent electrode layer.

[0068] The transparent conductive film of the present invention can be suitably used in applications requiring low resistance, such as light control elements, touch sensors, liquid crystal elements, photoelectric conversion elements, heat ray control members, antennas, electromagnetic wave shielding members, and image display devices.

[0069] REFERENCE SIGNS LIST 1 transparent conductive film 10 transparent resin substrate 20 functional layer 30 substrate 40 transparent electrode layer 40a lower layer 40b intermediate layer 40c upper layer

Claims

1. A transparent conductive film in which a transparent electrode layer containing indium oxide as a main component is formed on a flexible substrate, the transparent electrode layer having a structure in which at least three layers are laminated: a crystalline lower layer, an amorphous middle layer, and a crystalline upper layer, the grain boundaries are not continuous in the thickness direction across the middle layer, the lower layer has a thickness of 30 nm or more, and the middle layer has a thickness of 25 nm or less.

2. The transparent conductive film according to claim 1, wherein the transparent electrode layer has a film thickness of 100 nm or more.

3. The transparent conductive film according to claim 1 or 2, wherein the intermediate layer has a nitrogen content of 0.6 at % or more and 15 at % or less.

4. A method for producing a transparent conductive film according to claim 1 or 2, wherein the intermediate layer is formed by sputtering using a target containing indium oxide as a main component in an atmosphere in which the volume ratio of carrier gas to nitrogen gas is 250:10 to 250:300.

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